The above version of the API returns subjects related
to subjectId with one of the roles given
in roles path parameter. roles is a
comma-separate list of roles. For instance, if roles=parent,
then subjectId is the parent of the returned subjects.

This is the inverse of the first API. It returns the
subjects subjectId is related to with one of the roles
given in roles path parameter. For instance,
if roles=parent, then the returned subjects are the
parents of subjectId.